1. Field of the Invention
The present invention relates to a sheet ejection device which can align, in an orderly manner, sheets on a sheet output tray for all the types of sheets such as a thin sheet, a plain sheet, a thick sheet and the like, when these sheets are stacked on the sheet output tray by sequentially dropping, from a sheet ejection position, a plurality of sheets ejected from an image forming apparatus in a sheet ejecting direction.
2. Description of the Related Art
Recently, printers such as an inkjet printer, a stencil printer, a laser printer and the like and an image forming apparatus capable of forming images on a sheet by using a copier or the like perform printing and copying on a large amount of sheets.
When sheets are to be fed in this type of image forming apparatus, if, for example, friction occurs between the sheet and a feeding roller, static electricity collects on a sheet feeding path and the sheets.
As a result, when the plurality of sheets charged in the image forming apparatus is sequentially ejected toward the sheet output tray in the sheet ejecting apparatus installed on the sheet ejection side of the image forming apparatus, each of the ejected sheets leans on an end fence, a pair of side fences or the like provided around the sheet output tray due to the static electricity and remarkably deteriorates orderliness of the ejected sheets on the sheet output tray. In some cases, sheet jam is likely to occur.
Regarding the above-described problem, the applicant has already proposed a sheet ejection device which can favorably align sheets on the sheet output tray while removing electricity from each of the ejected sheets when sequentially ejecting the plurality of sheets charged in the image forming apparatus (For example, see Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2002-274741).
The sheet ejection device disclosed in Patent Literature 1 is provided with a sheet output tray, an end face, and a pair of side fences (not shown). On the sheet output tray, the plurality of sheets ejected from the image forming apparatus is stacked. The end fence abuts on a front end portion in the ejecting direction of each sheet stacked on the sheet output tray and regulates movement of the front end portion. The side fences regulate movement of end portions in the right-and-left direction while guiding, along the ejecting direction, the right and left end portions in the width direction crossing the ejecting direction of each sheet stacked on the sheet output tray. A conductive member using a metal material or the like is attached in an elongated manner on each of the inner surfaces of the end fence and the side fences, from an upper portion of the end fence and the side fences toward the sheet output tray, respectively. Each of the conductive members is earthed from the sheet output tray to the image forming apparatus side.
With the above-described configuration, when the plurality of sheets charged in the image forming apparatus is sequentially ejected toward the sheet output tray, the front end portion in the ejecting direction and the right and left end portions in the width direction of each ejected sheet are brought into contact with the conductive members attached to the inner surfaces of the end fence and the side fences, respectively, and electricity is removed from the ejected sheets. As a result, the sheets can be favorably aligned on the sheet output tray.
Generally, in an image forming apparatus and a sheet ejection device applied to the image forming apparatus, all the types of sheets such as a thin sheet having a basis weight of 60 g/m2 or less, a plain sheet having a basis weight of 60 g/m2 to 120 g/m2, a thick sheet having a basis weight of 120 g/m2 or more and the like can be applied. The weight of sheets increases in order of a thin sheet, a plain sheet, and a thick sheet, and rigidity of the sheets also increases in order of a thin sheet, a plain sheet, and a thick sheet.
In the sheet ejection device disclosed in Patent Literature 1, when the plurality of sheets charged in the image forming apparatus is sequentially ejected, the front end portion in the ejecting direction and the right and left end portions in the width direction of each ejected sheet get close to the conductive members attached to each of the inner surfaces of the end fence and the side fences, whereby the front end portion in the ejecting direction and the right and left end portions in the width direction of each ejected sheet are attracted to the conductive members, respectively, by Coulomb force at the time of electrostatic induction.
At this time, when a plain sheet or a thick sheet is used, even if the front end portion in the ejecting direction and the right and left end portions in the width direction of each of the charged plain sheets or thick sheets are attracted to the conductive members attached to the inner surfaces of each of the end fence and the side fences, respectively, the weight and rigidity of the plain sheet or thick sheet are large, and thus the charged plain sheet or thick sheet is brought into contact with the conductive members without being scarcely affected by the attracting force from these conductive members, and falls down while the electricity is removed therefrom. Therefore, since the plain sheet or thick sheet is stacked on the sheet output tray while its flat posture is maintained, the sheet ejection device disclosed in Patent Literature 1 can favorably align the plain sheet or thick sheet on the sheet output tray.
In contrast, in the case of using the thin sheet, the weight and rigidity of the thin sheet are small, and thus the front end portion in the ejecting direction and the right and left end portions in the width direction of the thin sheet are attracted to the conductive members to be inclined. Accordingly, since the thin sheet leans on the inner surfaces of the end face and the side fences and is stacked on the sheet output tray, the sheet ejection device disclosed in Patent Literature 1 cannot align the thin sheet on the sheet output tray favorably.
Moreover, when a thin sheet is used, the thin sheet to be subsequently ejected collides against or overlaps with the thin sheet leaning on the inner surfaces of the end fence and the side fences, which might cause an ejected sheet jam in some cases.